1.1.5 Types of Formula
Explain the terms empirical formula and molecular
formula.
Calculate empirical and molecular formulae.
page 12 - 13
1.1.5
1
USEFUL DEFINITIONS
Element
A substance which cannot be split into anything simpler by chemical means.
Atom
The smallest part of an element that can take part in a chemical reaction.
Molecule
The smallest particle of a compound (a combination of two or more elements).
It is also the name given to the smallest part of those elements which do not exist
as atoms in the free state i.e.
hydrogen
nitrogen
chlorine
iodine
H2
N2
Cl2
I2
oxygen
fluorine
bromine
O2
F2
Br2
N.B. ionic compounds (e.g. sodium chloride) do not exist as molecules.
page 12 - 13
1.1.5
2
USEFUL DEFINITIONS
Ion
The name given to any electrically charged atom or molecule.
• positively charged ions are known as cations
• negatively charged ions are known as anions
Like charges repel but unlike (opposite) charges attract. If the sum of all the
positive charges is equal and opposite to all the negative charges then the
species will be neutral (no overall charge).
Symbol
A symbol represents one atom, or one mole, of an element.
page 12 - 13
1.1.5
3
USEFUL DEFINITIONS
Formula
A formula represents one molecule of a compound, or the simplest ratio of the
ions present. As with symbols, a formula represents a single particle or one mole
of particles.
The number of atoms or groups of atoms in a formula is given by putting a small
number just below and behind the symbol(s). As the appearance of a symbol
indicates one atom is present, a 1 isn’t written (you put NaBr not Na1Br1).
In some formulae brackets are used to avoid ambiguity. Aluminium sulphate has
the formula Al2(SO4)3 to show that there are two Al’s to every three SO4‘s. Without
the brackets it would appear as though there were forty three O’s i.e. Al2SO43.
page 12 - 13
1.1.5
4
USEFUL DEFINITIONS
Valency
A numerical measure of the combining power of an atom / ion.
Historically, it was the number of hydrogen atoms which will combine with one
atom, or group of atoms.
Atom
C
N
O
Cl
Valency
4
3
2
1
Compound
CH4
NH3
H2O
HCl
It is also the number of positive (+) or negative (-) charges on an ion.
Many elements (e.g. iron) have more than one valency. To avoid ambiguity, a
number appears in brackets after the name e.g. iron(III); this is the oxidation
number and can be used to give you the valency.
page 12 - 13
1.1.5
5
CONSTRUCTION OF FORMULAE
Methods
Several methods are available, choose the one which suits you, or the situation,
best. Magnesium chloride is used as an example.
1.
Balance the number of ionic charges. All compounds are electrically
neutral so the number of positive and negative charges must balance.
Magnesium ions are Mg2+, chloride ions Cl¯. You need two Cl¯ ions to
balance the 2+ ion of magnesium. Therefore the formula will be MgCl2.
magnesium ion
chloride ion
Cl ¯
Mg2+
Cl ¯
page 12 - 13
Mg2+
1.1.5
Cl ¯
6
CONSTRUCTION OF FORMULAE
Methods
Several methods are available, choose the one which suits you, or the situation,
best. Magnesium chloride is used as an example.
2.
Use “hooks”. The valency is the number of “hooks” an element or group has.
All hooks must be joined up so there are no spares.
Magnesium has two “hooks”, — Mg — , chlorine has one, Cl — . Join up all
“hooks”; this gives you Cl — Mg — Cl . The formula is thus MgCl2.
page 12 - 13
1.1.5
7
FORMULAE AND EQUATIONS – TEST QUESTIONS
Q.3 How many atoms of each type are in the following ?
a) H2O
H= 2
O= 1
b) H2SO4
H= 2
O= 4
S = 1
c) (NH4)2SO4
H= 8
N= 2
O = 4
S = 1
d) CuSO4.5H2O
H = 10
O= 9
S = 1
Cu = 1
e) 2 NaOH
H= 2
O= 2
Na = 2
f) 3 Ca(OH)2
H= 6
O= 6
Ca = 3
g) 2 Na2HPO4
H= 2
O= 8
Na = 4
h) 2 NH4Al(SO4)2.12H2O
H = 56
N= 2
O = 40 Al = 2
page 12 - 13
1.1.5
P = 2
S= 4
8
FORMULAE AND EQUATIONS – TEST QUESTIONS
Q.3 How many atoms of each type are in the following ?
a) H2O
H= 2
O= 1
b) H2SO4
H= 2
O= 4
S = 1
c) (NH4)2SO4
H= 8
N= 2
O = 4
S = 1
d) CuSO4.5H2O
H = 10
O= 9
S = 1
Cu = 1
e) 2 NaOH
H= 2
O= 2
Na = 2
f) 3 Ca(OH)2
H= 6
O= 6
Ca = 3
g) 2 Na2HPO4
H= 2
O= 8
Na = 4
h) 2 NH4Al(SO4)2.12H2O
H = 56
N= 2
O = 40 Al = 2
page 12 - 13
1.1.5
P = 2
S= 4
9
FORMULAE AND EQUATIONS – TEST QUESTIONS
Q.3 How many atoms of each type are in the following ?
a) H2O
H= 2
O= 1
b) H2SO4
H= 2
O= 4
S = 1
c) (NH4)2SO4
H= 8
N= 2
O = 4
S = 1
d) CuSO4.5H2O
H = 10
O= 9
S = 1
Cu = 1
e) 2 NaOH
H= 2
O= 2
Na = 2
f) 3 Ca(OH)2
H= 6
O= 6
Ca = 3
g) 2 Na2HPO4
H= 2
O= 8
Na = 4
h) 2 NH4Al(SO4)2.12H2O
H = 56
N= 2
O = 40 Al = 2
page 12 - 13
1.1.5
P = 2
S= 4
10
FORMULAE AND EQUATIONS – TEST QUESTIONS
Q.3 How many atoms of each type are in the following ?
a) H2O
H= 2
O= 1
b) H2SO4
H= 2
O= 4
S = 1
c) (NH4)2SO4
H= 8
N= 2
O = 4
S = 1
d) CuSO4.5H2O
H = 10
O= 9
S = 1
Cu = 1
e) 2 NaOH
H= 2
O= 2
Na = 2
f) 3 Ca(OH)2
H= 6
O= 6
Ca = 3
g) 2 Na2HPO4
H= 2
O= 8
Na = 4
h) 2 NH4Al(SO4)2.12H2O
H = 56
N= 2
O = 40 Al = 2
page 12 - 13
1.1.5
P = 2
S= 4
11
FORMULAE AND EQUATIONS – TEST QUESTIONS
Q.3 How many atoms of each type are in the following ?
a) H2O
H= 2
O= 1
b) H2SO4
H= 2
O= 4
S = 1
c) (NH4)2SO4
H= 8
N= 2
O = 4
S = 1
d) CuSO4.5H2O
H = 10
O= 9
S = 1
Cu = 1
e) 2 NaOH
H= 2
O= 2
Na = 2
f) 3 Ca(OH)2
H= 6
O= 6
Ca = 3
g) 2 Na2HPO4
H= 2
O= 8
Na = 4
h) 2 NH4Al(SO4)2.12H2O
H = 56
N= 2
O = 40 Al = 2
page 12 - 13
1.1.5
P = 2
S= 4
12
FORMULAE AND EQUATIONS – TEST QUESTIONS
Q.3 How many atoms of each type are in the following ?
a) H2O
H= 2
O= 1
b) H2SO4
H= 2
O= 4
S = 1
c) (NH4)2SO4
H= 8
N= 2
O = 4
S = 1
d) CuSO4.5H2O
H = 10
O= 9
S = 1
Cu = 1
e) 2 NaOH
H= 2
O= 2
Na = 2
f) 3 Ca(OH)2
H= 6
O= 6
Ca = 3
g) 2 Na2HPO4
H= 2
O= 8
Na = 4
h) 2 NH4Al(SO4)2.12H2O
H = 56
N= 2
O = 40 Al = 2
page 12 - 13
1.1.5
P = 2
S= 4
13
FORMULAE AND EQUATIONS – TEST QUESTIONS
Q.3 How many atoms of each type are in the following ?
a) H2O
H= 2
O= 1
b) H2SO4
H= 2
O= 4
S = 1
c) (NH4)2SO4
H= 8
N= 2
O = 4
S = 1
d) CuSO4.5H2O
H = 10
O= 9
S = 1
Cu = 1
e) 2 NaOH
H= 2
O= 2
Na = 2
f) 3 Ca(OH)2
H= 6
O= 6
Ca = 3
g) 2 Na2HPO4
H= 2
O= 8
Na = 4
h) 2 NH4Al(SO4)2.12H2O
H = 56
N= 2
O = 40 Al = 2
page 12 - 13
1.1.5
P = 2
S= 4
14
FORMULAE AND EQUATIONS – TEST QUESTIONS
Q.3 How many atoms of each type are in the following ?
a) H2O
H= 2
O= 1
b) H2SO4
H= 2
O= 4
S = 1
c) (NH4)2SO4
H= 8
N= 2
O = 4
S = 1
d) CuSO4.5H2O
H = 10
O= 9
S = 1
Cu = 1
e) 2 NaOH
H= 2
O= 2
Na = 2
f) 3 Ca(OH)2
H= 6
O= 6
Ca = 3
g) 2 Na2HPO4
H= 2
O= 8
Na = 4
h) 2 NH4Al(SO4)2.12H2O
H = 56
N= 2
O = 40 Al = 2
page 12 - 13
1.1.5
P = 2
S= 4
15
CONSTRUCTION OF FORMULAE
Methods
Several methods are available
Switching the valency numbers if two valencies are different.
• Don’t write in a 1
• cancel any combination of numbers which can be reduced
e.g. Mg2O2 will become MgO
the valency of magnesium is two, so multiply chlorine by two
the valency of chlorine is one, so multiply magnesium by one to give Mg1Cl2
the formula will be
MgCl2.
page 12 - 13
1.1.5
16
CONSTRUCTION OF FORMULAE
example: aluminium sulphate
• the valency of aluminium is 3 and that of sulphate is 2
• they will combine in the ratio of 2 aluminiums to 3 sulphates
[i.e. 2x3 = 3x2]
• the formula will be Al2(SO4)3. [Notice the use of brackets]
Al 3+
SO4 2-
Al2(SO4)3
page 12 - 13
1.1.5
17
CONSTRUCTION OF FORMULAE
It is useful to learn some formulae...
Acids
hydrochloric acid
sulphuric acid
HCl
H2SO4
Gases
ammonia
NH3
carbon monoxide CO
sulphur dioxide
SO2
page 12 - 13
nitric acid
ethanoic acid
HNO3
CH3COOH
carbon dioxide
methane
CO2
CH4
1.1.5
18
TABLE OF IONS
1
2
3
POSITIVE IONS (CATIONS)
hydrogen
H+
sodium
Na+
potassium
K+
lithium
Li+
rubidium
Rb+
caesium
Cs+
copper(I)
Cu+
silver(I)
Ag+
ammonium
NH4+
NEGATIVE IONS (ANIONS)
chloride
Cl¯
bromide
Br¯
iodide
I¯
hydroxide
OH¯
nitrate(v)
NO3¯
(Nitrite)
nitrate(III)
NO2¯
hydrogencarbonate(IV) HCO3¯
hydrogensulphate(vi) HSO4¯
Chlorate (I)
ClO¯
Chlorate(V)
ClO3¯
calcium
barium
magnesium
zinc
iron(II)
cobalt
manganese(II)
tin(II)
copper(II)
Ca2+
Ba2+
Mg2+
Zn2+
Fe2+
Co2+
Mn2+
Sn2+
Cu2+
sulphate(vi)
sulphate (iv)
sulphide
oxide
carbonate(iv)
manganate (vii)
Chromate(VI)
Dichromate(VI)
SO42SO32- (Sulphite)
S2O2CO32MnO4CrO42Cr2O72-
aluminium
iron(III)
Al3+
Fe3+
phosphate (xi)
PO4319
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
H2O
CO2
NH3
O2
H2
SO2
SO3
HCl
HI
HF
CH4
H2S
HBr
H2SO4
HNO3
NaCl
NaNO3
Na2CO3
NaOH
Na2SO4
1
2
Water
Carbon dioxide (carbon IV oxide)
3
4
Ammonia
Oxygen
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
Hydrogen
Sulphur
Sulphur
Hydrogen
Hydrogen
Hydrogen
Methane
Hydrogen
Hydrogen
Sulphuric
Nitric
Sodium
Sodium
Sodium
Sodium
Sodium
page 12 - 13
molecule
molecule
dioxide
trioxide
chloride
iodide
fluoride
sulphide
bromide
Acid
acid
chloride
Nitrate (V)
Carbonate
hydroxide
sulphate
1.1.5
(Sulphur IV oxide)
(Sulphur VI oxide)
Hydrogen Sulphate (VI)
Hydrogen Nitrate(v)
(V)
(VI)
20
21
CaCl2
22
Ca(NO3)2
23
Ca(OH)2
24
CaSO4
25
BaCl2
26
AlCl3
27
Al(NO3)3
28
Al2(SO4)3
29
FeSO4
30
31
32
33
34
35
36
37
38
39
40
FeCl2
FeCl3
Fe2(SO4)3
PbO
PbO2
Pb(NO3)2
PbCl2
PbSO4
Cu(NO3)2
CuCl
CuCl2
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
4012 - 13
page
Calcium
chloride
Calcium
nitrate
Calcium
hydroxide
Calcium
sulphate
Barium
chloride
Aluminium
chloride
Aluminium
nitrate
Aluminium
sulphate
Iron(II)
sulphate
Iron(II)chloride
Iron(III)
chloride
Iron(III)
Lead(II)
Lead(IV)
Lead(II)
Lead(II)
Lead(II)
Copper(II)
Copper(I)
Copper(II)
1.1.5
Sulphate (VI)
oxide
oxide
Nitrate (V)
chloride
Sulphate (VI)
Nitrate (V)
chloride
chloride
(V)
(VI)
(V)
(VI)
(VI)
21
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
CuSO4
ZnCl2
AgNO3
NH4Cl
(NH4)2SO4
NH4VO3
KClO3
KIO3
NaClO
NaNO2
C2H6
C4H10
C8H18
(NH4)2CO3
KMnO4
K2CrO4
KHCO3
KI
Co(NO3)2
KAt
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60- 13
page 12
Copper(II)
Zinc
Silver
Ammonium
Ammonium
Ammonium
Potassium
Potassium
Sodium
Sodium
Ethane
Butane
Octane
Ammonium
Potassium
Potassium
Potassium
Potassium
Cobalt(II)
Potassium
1.1.5
Sulphate (VI)
chloride
Nitrate (V)
chloride
Sulphate (VI)
vanadate(V)
chlorate(V)
Iodate (V)
chlorate(I)
Nitrate (III)
Carbonate (IV)
manganate(VII)
chromate(VI)
hydrogencarbonate(IV)
iodide
Nitrate (III)
astatide
22
THE STRUCTURE OF ATOMS
Q.
• Name the following
Sn2+
• Give the symbol of
lead(IV) scandium(III)
Sn4+
Sb3+
• What do you notice about the valency of elements in...
Group I
Group II
Group VII
page 12 - 13
1.1.5
23
FORMULAE AND EQUATIONS – TEST QUESTIONS
Q.1 Write out the correct formula for each of the following compounds.
a) sodium chloride
NaCl
b) magnesium sulphate(vi) MgSO4
c) calcium oxide
CaO
d) calcium chloride
CaCl2
e) copper(II) nitrate(v)
Cu(NO3)2
f) potassium sulphate(vi)
K2SO4
g) manganese(IV) oxide
MnO2
h) zinc carbonate(iv)
ZnCO3
i) aluminium oxide
Al2O3
j) aluminium sulphate(vi)
Al2(SO4)3
k) aluminium bromide
AlBr3
l) calcium hydroxide
Ca(OH)2
page 12 - 13
1.1.5
24
Exercise 1.1.5
Writing formulae from names
Use the data in the table to write the formulae of the following.
1 Sodium Chloride
2 Sodium Hydroxide
3 Sodium Carbonate
4 Sodium sulphate(vi)
5 Sodium Phosphate
6 Potassium Chloride
7 Potassium Bromide
8 Potassium Iodide
9 Potassium Hydrogen Carbonate
10 Potassium Nitrate (iii)
11 Magnesium Chloride
12 Magnesium Nitrate (v)
13 Magnesium Hydroxide
14 Magnesium Oxide
15 Magnesium Carbonate
16 Calcium Oxide
17 Calcium Chloride
18 Calcium Sulphate(vi)
19 Calcium Carbonate
page 12 - 13
1.1.5
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
NaCl
NaOH
Na2CO3
Na2SO4
Na3PO4
KCl
KBr
KI
KHCO3
KNO2
MgCl2
Mg(NO3)2
Mg(OH)2
MgO
MgCO3
CaO
CaCl2
CaSO4
CaCO3
BaCl2
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
25
BaSO4
AlCl3
Al2O3
Al(OH)
Al2(SO4
CuSO4
CuO
CuCl2
Cu(NO3
Cu2O
CuCl
Zn(NO3
ZnCO3
ZnO
AgCl
AgBr
AgI
AgNO3
Ag2O
Pb(NO3
20 Barium Chloride
21 Barium Sulphate(vi)
22 Aluminium Chloride
23 Aluminium Oxide
24 Aluminium Hydroxide
25 Aluminium Sulphate(vi)
26 Copper(II) Sulphate(vi)
27 Copper(II) Oxide
28 Copper(II) Chloride
29 Copper(II) Nitrate (v)
30 Copper(I) Oxide
31 Copper(I) Chloride
32 Zinc Nitrate (v)
33 Zinc Carbonate
34 Zinc Oxide
35 Silver Chloride
36 Silver Bromide
37 Silver Iodide
38 Silver Nitrate (v)
39 Silver Oxide
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
NaCl
NaOH
Na2CO3
Na2SO4
Na3PO4
KCl
KBr
KI
KHCO3
KNO2
MgCl2
Mg(NO3)2
Mg(OH)2
MgO
MgCO3
CaO
CaCl2
CaSO4
CaCO3
BaCl2
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
BaSO4
AlCl3
Al2O3
Al(OH)3
Al2(SO4)3
CuSO4
CuO
CuCl2
Cu(NO3)2
Cu2O
CuCl
Zn(NO3)2
ZnCO3
ZnO
AgCl
AgBr
AgI
AgNO3
Ag2O
Pb(NO3)2
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
PbCO3
PbO
PbO2
PbCl2
PbCl4
PbS
SnCl2
SnCl4
FeSO4
FeCl2
Fe2(SO4)3
FeCl3
Fe(OH)3
Fe(OH)2
NH4Cl
(NH4)2CO3
NH4OH
NH4NO3
(NH4)2SO4
(NH4)3PO4
40 Lead(II) Nitrate (v)
page 12 - 13
1.1.5
26
41 Lead(II) Carbonate
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
NaCl
NaOH
43 Lead(IV) Oxide
Na2CO3
44 Lead(II) Chloride
Na2SO4
45 Lead(IV) Chloride
Na3PO4
46 Lead(II) Sulphide
KCl
47 Tin(II) Chloride
KBr
48KI
Tin(IV) Chloride
49KHCO
Iron(II) Sulphate(vi)
3
50KNO
Iron(II)2Chloride
51MgCl
Iron(III)2Sulphate(vi)
52Mg(NO
Iron(III) Chloride
3)2
2
53Mg(OH)
Iron(III) Hydroxide
54MgO
Iron(II) Hydroxide
3 Chloride
55MgCO
Ammonium
56CaO
Ammonium Carbonate
CaCl2
57 Ammonium Hydroxide
CaSO4
58 Ammonium Nitrate (v)
CaCO3
59 Ammonium Sulphate(vi)
BaCl2
42 Lead(II) Oxide
60 Ammonium Phosphate (xi)
61 Phosphorus Trichloride
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
BaSO4
AlCl3
Al2O3
Al(OH)3
Al2(SO4)3
CuSO4
CuO
CuCl2
Cu(NO3)2
Cu2O
CuCl
Zn(NO3)2
ZnCO3
ZnO
AgCl
AgBr
AgI
AgNO3
Ag2O
Pb(NO3)2
page 12 - 13
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1.1.5
PbCO3
PbO
PbO2
PbCl2
PbCl4
PbS
SnCl2
SnCl4
FeSO4
FeCl2
Fe2(SO4)3
FeCl3
Fe(OH)3
Fe(OH)2
NH4Cl
(NH4)2CO3
NH4OH
NH4NO3
(NH4)2SO4
(NH4)3PO4
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
PCl3
PCl5
P2O3
P2O5
H3PO4
H2SO4
HNO3
HCl
CCl4
SiCl4
SiO2
SO2
SO3
H2S
Cl2O
NO2
NO
CO2
CO
HOH/H2O
27
3
3
O3)2
H)2
3
62 Phosphorus Pentachloride
4
21 BaSO
63 Phosphorus
Trioxide
41
3
22 AlCl
42
64 Phosphorus
Pentoxide
23 Al2O3
43
65 Hydrogen Phosphate (xi) (Phosphoric Acid)
24 Al(OH)3
44
66 Hydrogen Sulphate(vi) (Sulphuric Acid)
25 Al2(SO4)3
45
67 Hydrogen Nitrate (v) (Nitric Acid)
26 CuSO4
46
68 Hydrogen
Chloride (Hydrochloric Acid)
27 CuO
47
2
28 CuCl
48
69 Carbon
Tetrachloride
Cu(NO3)2
29 Tetrachloride
49
70 Silicon
30 Cu2O
50
71 Silicon Dioxide
31 CuCl
51
72 Sulphur Dioxide
32 Zn(NO3)2
52
73 Sulphur Trioxide
33 ZnCO3
53
74 Hydrogen
Sulphide
34 ZnO
54
75 Chlorine(I)
Oxide
35 AgCl
55
36 AgBr
56
76 Nitrogen
Dioxide
37 AgI
57
77 Nitrogen
Monoxide
38 AgNO3
58
78 Carbon Dioxide
39 Ag2O
59
79 Carbon Monoxide
40 Pb(NO3)2
60
PbCO3
PbO
PbO2
PbCl2
PbCl4
PbS
SnCl2
SnCl4
FeSO4
FeCl2
Fe2(SO4)3
FeCl3
Fe(OH)3
Fe(OH)2
NH4Cl
(NH4)2CO3
NH4OH
NH4NO3
(NH4)2SO4
(NH4)3PO4
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
PCl3
PCl5
P2O3
P2O5
H3PO4
H2SO4
HNO3
HCl
CCl4
SiCl4
SiO2
SO2
SO3
H2S
Cl2O
NO2
NO
CO2
CO
HOH/H2O
80 Hydrogen Hydroxide
page 12 - 13
1.1.5
28
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
NaCl
NaOH
Na2CO3
Na2SO4
Na3PO4
KCl
KBr
KI
KHCO3
KNO2
MgCl2
Mg(NO3)2
Mg(OH)2
MgO
MgCO3
CaO
CaCl2
CaSO4
CaCO3
BaCl2
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
BaSO4
AlCl3
Al2O3
Al(OH)3
Al2(SO4)3
CuSO4
CuO
CuCl2
Cu(NO3)2
Cu2O
CuCl
Zn(NO3)2
ZnCO3
ZnO
AgCl
AgBr
AgI
AgNO3
Ag2O
Pb(NO3)2
page 12 - 13
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
1.1.5
PbCO3
PbO
PbO2
PbCl2
PbCl4
PbS
SnCl2
SnCl4
FeSO4
FeCl2
Fe2(SO4)3
FeCl3
Fe(OH)3
Fe(OH)2
NH4Cl
(NH4)2CO3
NH4OH
NH4NO3
(NH4)2SO4
(NH4)3PO4
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
PCl3
PCl5
P2O3
P2O5
H3PO4
H2SO4
HNO3
HCl
CCl4
SiCl4
SiO2
SO2
SO3
H2S
Cl2O
NO2
NO
CO2
CO
HOH/H2O
29
1
H2O
2
CO2
3
NH3
4
O2
5
H2
6
SO2
7
SO3
8
HCl
9
HI
10
HF
11
CH4
12
H2S
13
HBr
14
H2SO4
15
HNO3
16
NaCl
17
NaNO3
18
Na2CO3
19
NaOH
20
Na2SO4
Exercise 1.1.5 Formula to Names
page 12 - 13
1.1.5
30
21
CaCl2
22
Ca(NO3)2
23
Ca(OH)2
24
CaSO4
25
BaCl2
26
AlCl3
27
Al(NO3)3
28
Al2(SO4)3
29
FeSO4
30
FeCl2
31
FeCl3
32
Fe2(SO4)3
33
PbO
34
PbO2
35
Pb(NO3)2
page 12 - 13
1.1.5
31
36
PbCl2
37
PbSO4
38
Cu(NO3)2
39
CuCl
40
CuCl2
41
CuSO4
42
ZnCl2
43
AgNO3
44
NH4Cl
45
(NH4)2SO4
46
NH4VO3
47
KClO3
48
KIO3
49
NaClO
50
NaNO2
page 12 - 13
(V is Vanadium)
1.1.5
32
51
C2H6
52
C4H10
53
C8H18
54
(NH4)2CO3
55
KMnO4
56
K2CrO4
57
KHCO3
58
KI
59
Co(NO3)2
60
KAt
page 12 - 13
1.1.5
33
1
Water
31
Iron(III)
chloride
2
Carbon dioxide
32
Iron(III)
sulphate
3
Ammonia
33
Lead(II)
oxide
4
Oxygen
34
Lead(IV)
oxide
5
Hydrogen
35
Lead(II)
nitrate
6
Sulphur
dioxide
(or IV oxide)
36
Lead(II)
chloride
7
Sulphur
trioxide
(or VI oxide)
37
Lead(II)
sulphate
8
Hydrogen
chloride
38
Copper(II)
nitrate
9
Hydrogen
iodide
39
Copper(I)
chloride
10
Hydrogen
fluoride
40
Copper(II)
chloride
11
Methane
41
Copper(II)
sulphate
12
Hydrogen
sulphide
42
Zinc
chloride
13
Hydrogen
bromide
43
Silver
nitrate
14
Sulphuric
acid
44
Ammonium
chloride
15
Nitric
acid
45
Ammonium
sulphate
16
Sodium
chloride
46
Ammonium
vanadate(V)
17
Sodium
nitrate
47
Potassium
chlorate(V)
18
Sodium
carbonate
48
Potassium
iodate
19
Sodium
hydroxide
49
Sodium
chlorate(I)
20
Sodium
sulphate
50
Sodium
nitrite
21
Calcium
chloride
51
Ethane
22
Calcium
nitrate
52
Butane
23
Calcium
hydroxide
53
Octane
24
Calcium
sulphate
54
Ammonium
carbonate
25
Barium
chloride
55
Potassium
manganate(VII)
26
Aluminium
chloride
56
Potassium
chromate(VI)
27
Aluminium
nitrate
57
Potassium
hydrogencarbonate
28
Aluminium
sulphate
58
Potassium
iodide
29
Iron(II)
sulphate
59
Cobalt(II)
nitrate
30
Iron(II)chloride
60
Potassium
astatide
page 12 - 13
1.1.5
34
1.1.5 – Types of formula
EMPIRICAL AND MOLECULAR FORMULAE
Empirical formula
The empirical formula of a compound is the formula which shows the
simplest whole-number ratio in which the atoms in that compound exist.
It can be calculated if the composition by mass of the compound is known.
Molecular formula
The molecular formula of a substance is the formula which shows the
number of each type of atom in the one molecule of that substance.
It applies only to molecular substances, and can be deduced if the
empirical formula and molar mass of the compound are known.
The molecular formula is always a simple whole number multiple of the
empirical formula.
page 12 - 13
1.1.5
35
Example 1
a substance contains 85.8% carbon and 14.2% hydrogen, by mass
what is its empirical formula?
Mole ratio = 85.8
12
:
14.2
1
=
7.15
7.15
:
:
14.2
7.15
=
1
:
2
so empirical formula = CH2
If its relative molecular mass is 56, what is its molecular formula?
RMM = 56 = (CH2) so 14n = 56 and n = 56/14 = 4
Molecular formula = C4H8
page 12 - 13
1.1.5
36
It is also possible to calculate the percentage composition by mass of a substance, if
its empirical or molecular formula is known.
Example 1
What is the percentage composition by mass of ethanoic acid, C2H4O2?
RMM = 60
% C = (12 x 2)/60 x 100
= 40.0%
% H = (1 x 4)/60 x 100
= 6.67%
%O = (16 x 2)/60 x 100
= 53.3%
page 12 - 13
1.1.5
37
empirical and molecular formulae
1. A compound contains C 62.08%, H 10.34% and O 27.58% by mass. Find its
empirical formula and its molecular formula given that its relative molecular mass
is 58.
C3H6O
2. Find the empirical formula of the compound containing C 22.02%, H 4.59% and
Br 73.39% by mass.
C2H5Br
3. A compound containing 85.71% C and 14.29% H has a relative molecular mass of
56. Find its molecular formula.
C4H8
4. A compound containing 84.21% carbon and 15.79% hydrogen by mass has a
relative molecular mass of 114. Find its molecular formula.
C8H18
5. Analysis of a hydrocarbon showed that 7.8 g of the hydrocarbon contained 0.6 g of
hydrogen and that the relative molecular mass was 78. Find the molecular formula
of the hydrocarbon.
C6H6
6. 3.36 g of iron join with 1.44 g of oxygen in an oxide of iron. What is the empirical
formula of the oxide?
Fe2O3
7. What is the percentage composition of SiCl4?
16.6 % Si, 83.4 % Cl
8. What is the mass of sulphur in 1 tonne of H2SO4?
page 12 - 13
1.1.5
327 kg
38
1. C3H6O
2. C2H5Br
3. C4H8
4. C8H18
5. C6H6
6. Fe2O3
7. 16.6 % Si, 83.4 % Cl
8. 327 kg
page 12 - 13
1.1.5
39
1.1.5 Tasks
Write out these Key definitions
The empirical formula is . .
A molecule is . .
The molecular formula is . .
Examiner tip is . . . .
Worksheets
Questions : 1, 2
page 12 - 13
1.1.5
40
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1.1.5
41
Amount of oxygen = 0.01731 mol
Amount copper = 0.03460 mol
page 12 - 13
1.1.5
42
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43
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44
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1.1.5
45
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46
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47
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1.1.5
48